Chemical vapor deposition has been extensively described in the literature (including patents) as a technique for depositing a thin metallic coating on a heated substrate. Basically, a heat decomposable volatile metal compound (usually an organometallic compound), which may be called the precursor, is contacted with a substrate which has been heated to a temperature above the decomposition temperature of the metal compound. The metallic coating may be a metal, metal mixture or alloy, or metal compound or mixture thereof, depending on the choice of precursor(s) and reaction conditions.
While the technique has been described with reference to most transition metals and to certain other metals (including copper) and metalloids (silicon, for example), commercial use of CVD for the most part has been confined to deposition of a few metals and metal compounds, such as silicon, tungsten, and certain III-V and II-VI compounds (denoting, respectively, a compound of a Group III metal and a Group V element, and a compound of a Group II metal and a Group VI element). The absence of suitable heat decomposable organometallic compound for elements other than those mentioned above appears to have limited the extension of CVD to the deposition of other metals or compounds.
It is known that copper forms the compound cyclopentadienyl triethylphosphine copper (I), having the formula C.sub.5 H.sub.5 CuP(C.sub.2 H.sub.5).sub.3, by the reaction of cyclopentadiene and triethylphosphine on cuprous oxide. A description of the compound is given by G. Wilkinson et al. in J. Inorganic and Nuclear Chemistry, 1956, Vol. 2, pp. 32-37. This white crystalline solid melts at 127.degree. C. and its volatility is very low (around 10.sup.-2 at 100.degree. C.). The melting point and the non-volatile nature of this compound make it unsuitable for chemical vapor desposition applications.
G. Ortaggi, in Journal of Organometallic Chemistry. vol.80, 1974, pp. 275-279, reports preparation of cyclopentadianyl triphenylphosphine gold (I), methylcyclopentadinyl triphenylphosphine gold (I), and cyclopentadienyl triethylphosphine gold (I) No melting points or volatility data are given, but based on their similarity to the analogous copper compound described in Wilkinson cited supra, it is believed that these compounds also would not be sufficiently volatile for use in chemical vapor deposition.